This application claims the priority of German patent document 10 2007 032 084.3, filed Jul. 9, 2007, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a collision and conflict avoidance system for autonomous unmanned air vehicles (UAVs).
The operation of UAVs requires that they can be incorporated seamlessly into civil and military air traffic. Especially if there is no contact with the ground station, the UAV has to be independently capable, while observing air traffic regulations, of avoiding potential collisions without infringing its own performance limits or flying into restricted airspaces.
In conventional piloted aircraft, the TCAS (Traffic Alert Collision Avoidance System) is customarily used for this purpose. It uses its sensor components that determine the relative position of other aircraft, and based on this information, assesses the collision risk, determines reactive avoidance commands, and proposes them to the human pilot in order to avoid short-term collisions.
In the “Free flight conflict detection and resolution analysis” method (Kroyel, Mueller, Hunter), a two-stage system (tactical, strategic) for conflict avoidance in air traffic is proposed, while the article “A Hybrid A* Automaton approach to online path planning with obstacle avoidance” by N. D. Richards, M. Sharma, D. G. Ward, in AIAA 2004-6229, pp. 1-17, 2004, suggests an A* path search based on movement segments. (In the field of computer science the notation “A*”, pronounced “A star”, refers to a known graph search algorithm that determines a least cost path from a starting node to a goal node, out of one or more possible goals.)
The following components are known from the literature:                A* algorithm                    P. E. Hart, N. J. Nilsson, B. Raphael, “Correction to: A Formal Basis for the Heuristic Determination of Minimum Cost Paths”, SIGART Newsletter, 37, pp. 28-29, 1972                        Path segments (Motion primitives)                    N. D. Richards, M. Sharma, D. G. Ward, “A Hybrid A*/Automation Approach to On-line Path Planning with Obstacle Avoidance”, AIAA 2004-6229, pp. 1-17, 2004                        Two-stage method “tactical” & “strategic”                    Free Flight Conflight Detection (Kroyel, Mueller, Hunter)                        TCAS                    ICAO Annex 10, “Surveillance Radar and Collision Avoidance Systems”, ICAO Annex 10 Vol. IV, 2002                        Conflict avoidance:                    Aircraft Separation Systems            Free Flight Conflight Detection (Kroyel, Mueller, Hunter)                        Collision avoidance, as such                    Multisensor based Fully Autonomous Non-Cooperative Collision Avoidance System for UAVs (Fasano et al)            Autonomous Collision Avoidance of flying Vehicles (Szu et al)            Sense And Avoid (SAA & Traffic Alert and Collision Avoidance System (TCAS) Integration for Unmanned Aerial Systems (UAS) (Portilla et al)            UAV TRAJECTORY DESIGN USING TOTAL FIELD COLLISION AVOIDANCE (Sigurd et al)                        
In contrast to the prior art, the collision and conflict avoidance system according to the invention uses available on-board sensors in order to make for itself an image of the surrounding airspace. The situation thus established is analyzed for imminent conflicts (collisions, TCAS violations, airspace violations). If a problem is detected, a search is initiated for avoidance options which, as far as possible, comply with statutory air traffic regulations. According to the invention, depending on the available time budget, either a short-term reactive algorithm by means of direct FCS (Flight Control System) commands, or a medium-term path planning algorithm (which determines a flight plan optimized under aeronautical and economical boundary conditions) may be used. After the danger has been avoided, the UAV is returned to the original route.
The two tiered method and system according to the invention (that is, reactive and/or path planning) offers the following advantages:
The introduction of an on-board system into autonomous UAVs for conflict and collision avoidance allows their use in civil and military airspace in parallel and transparently to conventional aircraft. Because it uses an on-board algorithm the system functions independently of a data link, and because the TCAS zones are taken into account the remaining air traffic is not disturbed unnecessarily. The hybrid (two tier) system makes it possible both to cover aspects critical for safety and to use more highly developed algorithms in order to take complicated boundary conditions into account when determining the avoidance course.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.